Well, I saw a lot of Decimators flying around the other weekend at a (not so) local tourney, and they seemed to do pretty well. There was certainly a lot of them, anyway.
It gives the Imperials an (expensive) turreted option, which while it might not be everyone's coup of tea adds a bit of diversity to the faction. It can take a lot of damage, but at the same time it doesn't like critical hits. And Oicunn ramming everything in his path looks like a lot of fun.
Fleet Officer is a beastly little Imperial upgrade card as well.
In short it's probably the third bowl of Imperial porridge - it's not too hot, it's not too cold, it's juuuuust right.